1. Field of the Invention
The invention relates to a thermal solvent oil recovery method utilizing hot visbroken produced crude oil as the solvent injected into the oil formation in order to reduce the viscosity of the oil remaining in the formation and thereby enhance recovery of the oil from the formation.
2. Background of the Invention
Current primary oil production practices fail to recover much of the oil originally in place in natural formations. As a consequence thereof, much effort has been devoted to devising so-called secondary recovery methods of improving the ultimate recovery of the oil in the formations.
Various methods for inducing the recovery of viscous oil from underground formations are in existance. One such method is miscible flooding wherein a solvent for the oil is introduced into the formation and driven through the formation to displace the oil toward a production well from which oil is recovered. The solvents employed in these processes are expensive and the cost of solvent flooding is usually excessive in relation to the oil production obtainable thereby.
In U.S. Pat. No. 3,080,918 to Natland there is disclosed a process for heating produced oil by means of a nuclear reactor and passing the heated oil into the oil formation to reduce the viscosity of the oil and stimulate its recovery. The nuclear reactor is positioned in the well through which the produced oil is injected into the formation.
U.S. Pat. No. 4,174,752 to Slater et al discloses a method for heating recovered crude oil by solar means at the site of recovery thereof and injecting at least a portion of such heated crude oil back into the oil formation in order to reduce the viscosity of oil remaining in the oil formation and thereby allow a greater recovery of crude oil from the formation.
The present method is an improved thermal solvent oil recovery method in that it subjects a portion of the produced crude oil to a visbreaking operation to produce a hot visbroken crude oil solvent having reduced viscosity and injecting the hot visbroken crude oil solvent into the formation to stimulate recovery of oil contained therein.